In urban or city environments as well as rural locations there is a need by various police, military and civilian activities to identify that a gun or weapon has been fired. There are systems and methods for detecting gunshots.
For example, U.S. Pat. Nos. 5,504,717 and 5,703,835 issued to Sharkey, et. al. disclose security systems for detecting and reporting gunshot events in which a variety of individual detection units are positioned on a plurality of remote, separate pole units. Each pole unit includes a microphone for sensing acoustic signals, a signal conditioning and threshold unit coupled to the microphone, a data acquisition and signal processing unit, a communication unit, and a power supply. The outputs from the pole units are transmitted to a central processor at a base station where time domain differencing techniques are employed to fix the location of the gunshot(s). The signal conditioning and thresholding unit includes a signal comparator for detecting when an output signal from the microphone exceeds a predetermined level, and a peak background level averager that receives signals from both an averager rise time constant circuit and an averager decay time circuit. The averager rise time and averager decay time circuits produce output signals that are representative of time factors, as measured for example in milliseconds, of the acoustic signals sensed by the microphones.
Another system for detecting gunshots or gunfire is set forth in a South African patent application (Application No. 935960 dated Aug. 16, 1993) by Robin L. Foxcroft of FoxCraft Controls. Disclosed is a system for detecting and locating the origin of sounds such as gunfire, and means for reporting the occurrence of such gunfire. The system includes at least one microphone to convert sound waveforms into an intermediate electrical signal, processing means for comparing the intermediate signal produced by the microphone against a known signal, and means for producing an output if the intermediate electrical signal is sufficiently similar to the known signal. Other features include a processing means capable of generating a Fourier transform of an intermediate electrical signal and of comparing the transformed intermediate signal against a Fourier transform a known gunshot, and a memory which stores the transforms of various known signals.
Another acoustic detection method and system for locating the source of a gunshot is set forth in U.S. Pat. No. 5,586,086 issued to Permuy, et.al. The system comprises an antenna having at least three microphones that are spaced apart from each other and connected via a microphone conditioning stage to a processing and display unit. The processing and display unit includes means for processing the signals and for determining the location and possible type of projectile being fired.
Acoustic detection circuits are also disclosed in U.S. Pat. Nos. 4,001,771 issued to Amrine; 4,083,031 issued to Pharo; 4,091,366 issued to Lavallee; 4,279,027 issued to Van Sloun; and 5,046,053 issued to Gilchrist.